The invention relates to methods and equipment for block encoders. As is well known, block encoders are frequently used for error correction. An example of a block encoder is a so-called turbo (en)coder, as disclosed in reference 1.
FIG. 1 is a block chart of a turbo encoder TE which is connected to a corresponding turbo decoder TD via a (transmission) channel. A typical turbo encoder conveys the original information directly to the channel. These bits are called systematic bits. Additionally, the turbo encoder adds redun-dancy (parity) with simple encoders 1 and 2, the latter of which is preceded by an interleaver P, which permutes the bits of the original information. However, details of the block encoder are not relevant for understanding the invention, and reference is made to relevant literature.
Unlike streaming encoders, block encoders process. one or more data blocks at a time. An input data block whose size exceeds the block size of the block encoder must be divided into smaller segments such that no segment is larger than the block size of the block encoder. This is why block encoders are particularly suitable for applications with a fixed input block size. A problem with block encoders is that they do not easily lend themselves to applications having a variable (dynamic) input block size. In other words, what to do with the last few segments of the input data block, remains an open question.
An object of the invention is to provide a mechanism for using block encoders with applications having a variable (dynamic) input block size. The mechanism should be generic in order to be applicable to a wide variety of block encoders.
This object is achieved with a method and equipment which are characterized by what is disclosed in the attached independent claims. Preferred embodiments of the invention are disclosed in the attached dependent claims.
A straightforward solution would be to fill the segment of the input data block to the block size of the block encoder. Assuming a block size of 8 kilobits (kb), a 14-kb input data block would be divided into a first segment of 8 kb and second (last) segment with a net size of 6 kb and 2 kb of fill (padding) bits. A benefit of this straightforward solution is that the block encoder does not have to adapt to varying input block sizes.
The invention is based on the idea that for an input data block whose size exceeds the block size of the block encoder:
1) before coding is started, the size of the input data block is determined; and
2) the input data block is divided into segments of approximately equal size such that no segment is larger than the block size of the block encoder.
An aspect of the invention is a segmentation device for segmenting an input data block for processing with a block encoder, wherein the block encoder is capable of processing consecutive coding blocks whose size has an upper limit which is smaller than the size of the input data block. The segmentation device is arranged to: determine the length of the input data block before applying any of its data to the block encoder; divide the input data block to a plurality of segments wherein all segments are of substantially equal size and no segment is larger than the upper limit; and to apply each segment to the block encoder.
According to a preferred embodiment of the invention, the input data block is divided into the least possible number of segments. In other words, the segments are as large as possible.
According to an alternative embodiment, the input data block is divided into 2n segments where n is a positive integer.
According to yet another preferred embodiment of the invention, if dividing the input data block produces a last segment which is shorter than the remaining segments, the input data block or the last segment is padded with a few fill bits until the length of the last segment equals that of the remaining segments. However, in contrast to the straightforward solution, the last segment is not padded to the full block size of the block encoder (unless the remaining segments happen to be of that size too).